Big Chemical Encyclopedia

Chemical substances, components, reactions, process design ...

Articles Figures Tables About

Homocysteine

Many disorders are associated with increased levels of total homocysteine. In this section, the basic biochemistry, clinical significance, and measurement of total homocysteine (tHcy) are summarized. [Pg.967]

Numerous studies have suggested an association between elevated levels of circulating homocysteine and various vascular and cardiovascular disorders. In addition, tHcy levels also are related to birth defects, pregnancy complications, psychiatric disorders,and mental impairment in the elderly. Clinically the measurement of tHcy is considered important (1) to diagnose homocystinuria, (2) to identify individuals with or at a risk of developing [Pg.967]

Although numerous studies have demonstrated a causal relationship between tHcy and CVD, there is still controversy about the clinical significance of this relationship as (1) the MTHFR 677C—polymorphism is a strong risk factor for increased tHcy but not for CVD (2) there is an apparent discrepancy between prospective and retrospective case-control studies and (3) there is a lack of data from controlled clinical trials.  [Pg.968]

Because of this concern over the clinical significance of the causal relationship between tHcy and Refsum and colleagues developed the following recommendations  [Pg.968]

Physiologically, homocysteine exists in reduced, oxidized, and protein-bound forms.Methods for tHcy were first introduced in the midl980s that resolved the problems related to the presence of multiple unstable Hey species in plasma by converting all Hey species into the reduced form, HcyH, which is measured as an indication of tHcy content. Consequently, modern methods require pretreatment of plasma or serum specimens with a reducing agent, such as dithioerythritol, dithiothreitol, mercap-toethanol, tributyl phosphine, and tris(2-carboxyl-ethyl) phosphine that converts all Hey species into the reduced form, HcyH, which is measured as an indication of tHcy content. [Pg.968]

Biosynthesis of cysteine. The sulfur is derived from methionine, and the carbon skeleton and amino group are derived from serine. [Pg.354]

Deficiencies of methionine adenosyltransferase, cystathionine 8-synthase, and cystathionine )/-lyase have been described. The first leads to hypermethioninemia but no other clinical abnormality. The second leads to hypermethioninemia, hyperhomocysteinemia, and homo-cystinuria. The disorder is transmitted as an autosomal recessive trait. Its clinical manifestations may include skeletal abnormalities, mental retardation, ectopia lentis (lens dislocation), malar flush, and susceptibility to arterial and venous thromboembolism. Some patients show reduction in plasma methionine and homocysteine concentrations and in urinary homocysteine excretion after large doses of pyridoxine. Homocystinuria can also result from a deficiency of cobalamin (vitamin B12) or folate metabolism. The third, an autosomal recessive trait, leads to cystathioninuria and no other characteristic clinical abnormality. [Pg.354]

Hereditary sulfite oxidase deficiency can occur alone or with xanthine oxidase deficiency. Both enzymes contain molybdenum (Chapter 27). Patients with sulfite oxidase deficiency exhibit mental retardation, major motor seizures, cerebral atrophy, and lens dislocation. Dietary deficiency of molybdenum (Chapter 37) can cause deficient activity of sulfite and xanthine oxidases. [Pg.354]

Cystinuria is a disorder of renal and gastrointestinal tract amino acid transport that also affects lysine, ornithine, and arginine. The four amino acids share a common transport mechanism (discussed above). Clinically, it presents as urinary stone disease because of the insolubility of cystine. In cystinosis, cystine crystals are deposited in tissues because of a transport defect in ATP-dependent cystine efflux from lysosomes (discussed above). [Pg.354]

Homocysteine is an amino acid not found in proteins. Its metabolism involves two pathways one is [Pg.354]


Homocysteine arises from dietary methionine. High levels of homocysteiae (hyperhomocysteinemia) are a risk factor for occlusive vascular diseases including atherosclerosis and thrombosis (81—84). In a controlled study, semm folate concentrations of <9.2 nmol/L were linked with elevated levels of plasma homocysteiae. Elevated homocysteine levels have beea associated also with ischemic stroke (9). The mechanism by which high levels of homocysteine produce vascular damage are, as of yet, aot completely uaderstood. lateractioa of homocysteiae with platelets or eadothehal cells has beea proposed as a possible mechanism. Clinically, homocysteine levels can be lowered by administration of vitamin B, vitamin B 2> foHc acid. [Pg.42]

Methylcobalamin is involved in a critically important physiological transformation, namely the methylation of homocysteine (8) to methionine (9) (eq. 2) catalyzed by A/ -methyltetrahydrofolate homocysteine methyltransferase. The reaction sequence involves transfer of a methyl group first from... [Pg.112]

Homocysteine has been identified as an independent risk factor for atherosclerosis (32) and thus metaboHc control over homocysteine levels has major health implications. [Pg.112]

The antiviral activity of (5)-DHPA in vivo was assessed in mice inoculated intranasaHy with vesicular stomatitis vims ( 5)-DHPA significantly increased survival from the infection. (5)-DHPA did not significantly reduce DNA, RNA, or protein synthesis and is not a substrate for adenosine deaminase of either bacterial or mammalian origin. However, (5)-DHPA strongly inhibits deamination of adenosine and ara-A by adenosine deaminase. Its mode of action may be inhibition of Vadenosyl-L-homocysteine hydrolase (61). Inhibition of SAH hydrolase results in the accumulation of SAH, which is a product inhibitor of Vadenosylmethionine-dependent methylation reactions. Such methylations are required for the maturation of vital mRNA, and hence inhibitors of SAH hydrolase may be expected to block vims repHcation by interference with viral mRNA methylation. [Pg.308]

Mechanistic aspects of the action of folate-requiring enzymes involve one-carbon unit transfer at the oxidation level of formaldehyde, formate and methyl (78ACR314, 8OMI2I6OO) and are exemplified in pyrimidine and purine biosynthesis. A more complex mechanism has to be suggested for the methyl transfer from 5-methyl-THF (322) to homocysteine, since this transmethylation reaction is cobalamine-dependent to form methionine in E. coli. [Pg.325]

Certain amino acids and their derivatives, although not found in proteins, nonetheless are biochemically important. A few of the more notable examples are shown in Figure 4.5. y-Aminobutyric acid, or GABA, is produced by the decarboxylation of glutamic acid and is a potent neurotransmitter. Histamine, which is synthesized by decarboxylation of histidine, and serotonin, which is derived from tryptophan, similarly function as neurotransmitters and regulators. /3-Alanine is found in nature in the peptides carnosine and anserine and is a component of pantothenic acid (a vitamin), which is a part of coenzyme A. Epinephrine (also known as adrenaline), derived from tyrosine, is an important hormone. Penicillamine is a constituent of the penicillin antibiotics. Ornithine, betaine, homocysteine, and homoserine are important metabolic intermediates. Citrulline is the immediate precursor of arginine. [Pg.87]

In addition, 1 mg of sterile S-2-hydroxyethyl-DL-homocysteine Is added to the tube and the tube is shaken on a rotary shaker at 280 cycles per minute at 25°C for seven days. [Pg.438]

In addition to the twenty amino acids commonly found in proteins, two others—selenocysteine and pyrrolysine—are found in some organisms, and more than 700 nonprotein amino acids are also found in nature. y-Amino-butyric acid (GABA), for instance, is found in the brain and acts as a neurotransmitter homocysteine is found in blood and is linked to coronary heart disease and thyroxine is found in the thyroid gland, where it acts as a hormone. [Pg.1020]

Methyl-tetrahydro folic acid is furthermore, together with vitamin B12 and B6, required to regenerate homocysteine (see Vitamin B12, Fig. 1). Homocysteine results when methionine is used as a substrate for methyl group transfer. During the last few years, homocysteine has been acknowledged as an independent risk factor in atherosclerosis etiology. Folic acid supplementation can help reduce elevated homocysteine plasma levels and is therefore supposed to reduce the risk of atherosclerosis as well [2]. [Pg.509]

N5-Methyltetrahydrofolate homocysteine methyl-transferase (= methionine synthase). This reaction is essential to restore tetrahydrofolate from N5-methyltetrahydrofolate (Fig. 2). [Pg.1291]

Relatively few reports have been published subsequently on the use of these reagents. Hope and coworkers99 have used sodium in liquid ammonia to cleave the benzyl sulphonyl derivatives of cysteamine, L-cysteine and L-homocysteine to prepare the corresponding sulphinic acids, as in equation (42). [Pg.944]

CxH Hg02, 62-38-4) see Phenylmcrcuric borate phenylmercuric hydroxide (C H HgO 100-57-2) see Phenylmercuric borate JV-[(phenylmethoxy)carbonylJ-DL-homocysteine acetate (ester)... [Pg.2433]

Enzymatic methylation of homocysteine (HSCHjCHjCHNHjCOOH) by methylcobalamin to give methionine (CH3SCH2CH2CHNH2COOH) was discovered in 1962 by Woods and co-workers, who also noticed the occurrence of a much slower, nonenzymatic reaction giving the same products. Methylcobinamide showed the same activity as the cobalamin in both the enzymatic and nonenzymatic reactions (72, 7/). It was subsequently discovered that HS, MeS , PhS , and w-BuS will dealkylate a variety of methyl complexes [DMG, DMG-BF2, DPG, G, salen, (DO)(DOH)pn, cobalamin] and even ethyl-Co(DMG)2 complexes to give the thioethers, and it was suggested that the reaction involved transfer of the carbonium ion to the attacking thiolate 161, 164), e.g.,... [Pg.426]


See other pages where Homocysteine is mentioned: [Pg.403]    [Pg.877]    [Pg.877]    [Pg.16]    [Pg.45]    [Pg.387]    [Pg.7]    [Pg.7]    [Pg.43]    [Pg.112]    [Pg.122]    [Pg.123]    [Pg.312]    [Pg.312]    [Pg.312]    [Pg.100]    [Pg.100]    [Pg.308]    [Pg.90]    [Pg.258]    [Pg.524]    [Pg.88]    [Pg.603]    [Pg.350]    [Pg.350]    [Pg.1020]    [Pg.1300]    [Pg.509]    [Pg.755]    [Pg.825]    [Pg.855]    [Pg.766]    [Pg.1484]    [Pg.2393]    [Pg.2433]    [Pg.439]   
See also in sourсe #XX -- [ Pg.212 ]

See also in sourсe #XX -- [ Pg.291 ]

See also in sourсe #XX -- [ Pg.185 , Pg.482 ]

See also in sourсe #XX -- [ Pg.80 , Pg.110 , Pg.183 ]

See also in sourсe #XX -- [ Pg.234 ]

See also in sourсe #XX -- [ Pg.222 ]

See also in sourсe #XX -- [ Pg.234 ]

See also in sourсe #XX -- [ Pg.110 ]

See also in sourсe #XX -- [ Pg.89 , Pg.91 ]

See also in sourсe #XX -- [ Pg.1211 ]

See also in sourсe #XX -- [ Pg.443 ]

See also in sourсe #XX -- [ Pg.68 , Pg.99 , Pg.147 ]

See also in sourсe #XX -- [ Pg.73 ]

See also in sourсe #XX -- [ Pg.455 ]

See also in sourсe #XX -- [ Pg.384 ]

See also in sourсe #XX -- [ Pg.140 ]

See also in sourсe #XX -- [ Pg.449 ]

See also in sourсe #XX -- [ Pg.434 ]

See also in sourсe #XX -- [ Pg.3 , Pg.3 , Pg.5 , Pg.5 ]

See also in sourсe #XX -- [ Pg.255 , Pg.256 , Pg.290 ]

See also in sourсe #XX -- [ Pg.255 , Pg.256 , Pg.290 ]

See also in sourсe #XX -- [ Pg.21 , Pg.34 ]

See also in sourсe #XX -- [ Pg.6 ]

See also in sourсe #XX -- [ Pg.597 ]

See also in sourсe #XX -- [ Pg.89 , Pg.91 ]

See also in sourсe #XX -- [ Pg.725 ]

See also in sourсe #XX -- [ Pg.22 ]

See also in sourсe #XX -- [ Pg.255 , Pg.256 , Pg.290 ]

See also in sourсe #XX -- [ Pg.243 , Pg.269 , Pg.272 ]

See also in sourсe #XX -- [ Pg.4 , Pg.4 , Pg.408 , Pg.412 ]

See also in sourсe #XX -- [ Pg.54 , Pg.112 ]

See also in sourсe #XX -- [ Pg.967 , Pg.967 ]

See also in sourсe #XX -- [ Pg.399 , Pg.408 , Pg.412 ]

See also in sourсe #XX -- [ Pg.97 , Pg.100 ]

See also in sourсe #XX -- [ Pg.26 , Pg.354 , Pg.923 ]

See also in sourсe #XX -- [ Pg.39 ]

See also in sourсe #XX -- [ Pg.148 ]

See also in sourсe #XX -- [ Pg.463 , Pg.473 , Pg.474 , Pg.476 ]

See also in sourсe #XX -- [ Pg.1063 ]

See also in sourсe #XX -- [ Pg.282 ]

See also in sourсe #XX -- [ Pg.154 ]

See also in sourсe #XX -- [ Pg.1313 ]

See also in sourсe #XX -- [ Pg.405 , Pg.416 , Pg.418 , Pg.420 ]

See also in sourсe #XX -- [ Pg.73 ]

See also in sourсe #XX -- [ Pg.68 , Pg.99 , Pg.147 ]

See also in sourсe #XX -- [ Pg.154 ]

See also in sourсe #XX -- [ Pg.30 , Pg.145 , Pg.163 ]

See also in sourсe #XX -- [ Pg.203 ]

See also in sourсe #XX -- [ Pg.455 ]

See also in sourсe #XX -- [ Pg.5 , Pg.8 ]

See also in sourсe #XX -- [ Pg.161 ]

See also in sourсe #XX -- [ Pg.31 , Pg.42 ]

See also in sourсe #XX -- [ Pg.513 ]

See also in sourсe #XX -- [ Pg.365 , Pg.366 , Pg.366 ]

See also in sourсe #XX -- [ Pg.244 ]

See also in sourсe #XX -- [ Pg.41 , Pg.44 , Pg.45 , Pg.54 ]

See also in sourсe #XX -- [ Pg.79 , Pg.82 , Pg.85 , Pg.94 ]

See also in sourсe #XX -- [ Pg.534 , Pg.668 ]

See also in sourсe #XX -- [ Pg.11 ]

See also in sourсe #XX -- [ Pg.283 , Pg.332 ]

See also in sourсe #XX -- [ Pg.139 , Pg.452 , Pg.545 , Pg.546 ]

See also in sourсe #XX -- [ Pg.2 , Pg.3 , Pg.566 , Pg.1352 ]

See also in sourсe #XX -- [ Pg.25 , Pg.35 , Pg.139 , Pg.354 , Pg.466 , Pg.467 , Pg.472 , Pg.476 , Pg.494 , Pg.497 , Pg.534 , Pg.743 ]

See also in sourсe #XX -- [ Pg.1143 , Pg.1246 , Pg.1268 , Pg.1321 ]

See also in sourсe #XX -- [ Pg.322 , Pg.362 ]

See also in sourсe #XX -- [ Pg.2 , Pg.794 ]

See also in sourсe #XX -- [ Pg.37 ]

See also in sourсe #XX -- [ Pg.243 , Pg.245 ]

See also in sourсe #XX -- [ Pg.34 , Pg.36 ]

See also in sourсe #XX -- [ Pg.390 ]

See also in sourсe #XX -- [ Pg.1160 ]

See also in sourсe #XX -- [ Pg.15 ]

See also in sourсe #XX -- [ Pg.192 ]

See also in sourсe #XX -- [ Pg.255 , Pg.256 ]

See also in sourсe #XX -- [ Pg.443 ]

See also in sourсe #XX -- [ Pg.27 , Pg.28 , Pg.30 , Pg.166 ]

See also in sourсe #XX -- [ Pg.571 , Pg.609 ]

See also in sourсe #XX -- [ Pg.101 ]

See also in sourсe #XX -- [ Pg.227 ]

See also in sourсe #XX -- [ Pg.290 ]

See also in sourсe #XX -- [ Pg.531 , Pg.532 , Pg.533 , Pg.534 ]

See also in sourсe #XX -- [ Pg.199 ]

See also in sourсe #XX -- [ Pg.365 , Pg.366 , Pg.366 ]

See also in sourсe #XX -- [ Pg.463 ]




SEARCH



5,10-methylenetetrahydrofolate homocysteine metabolism

5-Adenosyl-L-homocysteine

5-Adenosyl-L-homocysteine hydrolase

5-Methyltetrahydrofolate-homocysteine

5-Methyltetrahydrofolate-homocysteine methyltransferase

A-Methyltetrahydrofolate-homocysteine

Adenosine-homocysteine condensing

Adenosyl homocysteine

Amines with N-Acetyl Homocysteine Thiolactone

Amino acid degradation homocysteine

Amino acid homocysteine

Analysis of Homocysteine

Atherogenesis, homocysteine

Atherosclerosis homocysteine

Betaine-homocysteine

Betaine-homocysteine methylpherase

Betaine-homocysteine methyltransferase

Betaine-homocysteine methyltransferase BHMT)

Cardiovascular disease homocysteine

Cardiovascular disease, homocysteine vitamin

Citiolone homocysteine thiolactone

Connective tissue, homocysteine

Coronary artery disease homocysteine

Coronary heart disease homocysteine

Cysteine homocysteine disulfide

Cysteine homocysteine metabolism

Dimethylthetin-homocysteine

Dimethylthetin-homocysteine methylpherase

Endothelial cells homocysteine

Epidemiology homocysteine

Folate homocysteine and

Folates homocysteine metabolism

Folic acid homocysteine metabolism

Glutathione homocysteine

Heart disease, homocysteine

Homocysteine S-methyltransferase

Homocysteine accumulation

Homocysteine and Methionine

Homocysteine assay

Homocysteine asymmetric dimethylarginine

Homocysteine biosynthesis

Homocysteine biosynthesis control

Homocysteine biosynthesis enzymes

Homocysteine blood concentration

Homocysteine cobalamins

Homocysteine cognitive effect

Homocysteine conversion from methionine

Homocysteine cystathionine synthetase polymorphism

Homocysteine dementia

Homocysteine desulfhydrase

Homocysteine desulfhydrases

Homocysteine desulfuration

Homocysteine diseases affected

Homocysteine disulfide

Homocysteine elevated plasma concentrations

Homocysteine elevated serum levels

Homocysteine folate

Homocysteine from methionine

Homocysteine inflammation

Homocysteine lactone

Homocysteine lowering therapy

Homocysteine metabolism

Homocysteine metabolism AdoMet)

Homocysteine metabolism cobalamins

Homocysteine metabolism disorders

Homocysteine metabolism methionine synthase

Homocysteine metabolism pyridoxal-5 -phosphate

Homocysteine methionine formation

Homocysteine methylation

Homocysteine methylene tetrahydrofolate reductase

Homocysteine methyltransferase

Homocysteine methyltransferases

Homocysteine nicotinic acid

Homocysteine occurrence

Homocysteine oxidation

Homocysteine oxidative stress

Homocysteine plasma concentration

Homocysteine pregnancy

Homocysteine reactions

Homocysteine regulators

Homocysteine remethylation

Homocysteine renal disease

Homocysteine riboflavin

Homocysteine serum concentration

Homocysteine smooth muscle proliferation

Homocysteine stroke

Homocysteine studies

Homocysteine sulfonamide

Homocysteine sulfur oxidation

Homocysteine supplementation

Homocysteine synthase

Homocysteine synthesis

Homocysteine synthesis plants

Homocysteine thiolactone

Homocysteine toxicity

Homocysteine transmethylase

Homocysteine transmethylation

Homocysteine transsulfuration pathway

Homocysteine vitamin

Homocysteine with Liberation of Hydrogen Sulfide

Homocysteine, and cystathionine

Homocysteine, conversion to methionine

Homocysteine, folate deficiency, marker

Homocysteine, structure

Homocysteine-cysteine

Homocysteine-y-thiolactone

Homocystine, and homocysteine

Homoserine, Homocysteine, Methionine, and Derivatives

Hydrolases adenosyl homocysteine hydrolase

Hypertension, homocysteine

Hypertension, homocysteine vitamin D toxicity

Ischemic heart disease homocysteine

Isotretinoin homocysteine

Kidneys homocysteine

L-Homocysteine

L-Homocysteine metabolism

Methionine formation from homocysteine, vitamin

Methionine regeneration from homocysteine

Methionine to homocysteine

Methylenetetrahydrofolate reductase homocysteine metabolism

N-Acetyl homocysteine

N-Acetyl homocysteine immobilization

N-Acetyl homocysteine thiolactone

Nitric oxide homocysteine

Plasma homocysteine

Plasma total homocysteine

Platelet aggregation, vitamin homocysteine

Restenosis homocysteine

S-Adenosyl homocysteine

S-Guanosyl-L-homocystein

S-adenosyl-L-homocysteine

S-adenosyl-L-homocysteine (AdoHcy

S-adenosyl-L-homocysteine hydrolase

S-adenosyl-homocysteine hydrolase

Scanning homocysteine

Serum homocysteine

Subject homocysteine metabolism

Sulfide homocysteine formation

Sulfur-containing compounds homocysteine

Supplements homocysteine levels

Tetrahydrofolate homocysteine metabolism

Thiolation N-acetyl homocysteine

Thrombosis homocysteine

Total homocysteine

Total serum homocysteine levels

Vascular walls homocysteine

Vitamin homocysteine and

© 2024 chempedia.info